Electrodynamic transducers with flexible ferromagnetic flux paths



July 20, 1965 A. c. DAVIS ELECTRODYNAMIC TRANSDUCERS WITH FLEXIBLE FERROMAGNETIC FLUX PATHS Flled Dec 15 1959 4 1 l Q q q. a vwhowon npvn wowh m V INVENTOR. ARTHUR 6. DA V/6 A TTOR/VEY United States Patent Arthur Davis, 63.5 Via Lido Soud, Newport Beach, (Ialii. Filed Dec. 35, 1959, Ser. No. 859,647 Qlairns. (Cl. l79-1tltl.4l)

This invention pertains to new and improved transducers, more specifically to transducers utilizing variable reluctance in magnetic circuits.

The term transducer is commonly employed in a generic or broad sense to designate devices which are used in converting energy of one type into another type of energy. Thus, for example, a phonograph pickup is a type of transducer which is used to change mechanical energy into electrical energy. In the case of a phonograph pickup the mechanical energy is derived from the contact of a stylus or needle with a phonograph record, and the electrical energy produced by a transducer serving as a phonograph pickup may be in the form of a change of capacitance or the like depending upon the nature of the transducer employed. Because of the fact that transducers are used as devices allowin the conversion of energ from one form to another the basic principles of any type of transducer may be applied in a number of diilerent types of devices such as microphones, loud speakers and the like. Any transducer which is in tended for one application may usually be applied by appropriate modifications of a routine engineering nature to at least a number of other different types or applications.

A broad generalized object of this invention is to provide new and improved transducers. Another general object of this invention is to provide transducers which may be easily and conveniently constructed at a comparatively nominal cost. A further broad object of this invention is to provide transducers which may be easily used and which are quite reliable in operation. A more specific object of the present invention is to provide transducers which utilize variable reluctance in a magnetic circuit. A related object of the present invention is to provide transducers of this type in which the change in reluctance is a result of motion or mechanical force.

These and other objects of the present invention will be fully apparent to those skilled in the art to which the invention pertains from a detailed consideration of the remainder of this description including the appended claims and the accompanying drawing in which:

FIG. 1 is a perspective view of a transducer of this invention;

FIG. 2 is a crosssectional view taken at line 2-2 of ducer of this invention;

PEG. 5 is a cross-sectional view taken at line 55 of PEG 4 FIG. 6 is a perspective View of a further modified transducer or" this invention;

FIG. 7 is a cross-sectional view taken at line 7-7 of FlG. 6;

FIG. 8 is a cross-sectional view taken at line 88 of PEG. 6.

The accompanying drawing is primarily intended so as to clearly illustrate several presently preferred embodiments or forms of this invention. Those skilled in the art of transducers will realize from a consideration of the drawing and of the remainder of this specification that the basic features or principles of this invention as herein described may be embodied within other diilerently appearing and differently employed transducers through the exercise of routine design or engineering skill.

As an aid to understanding this invention it can be stated in essentially summary form that it concerns transducers, each of which is formed so as to include a flexible core having ends, means for rigidly mounting one of the ends of this core, means for flexing the core secured to the other end of the core, coil means positioned around the core between these'ends, and magnetic means for creating a magnetic field within the core and within the coil, the permeability of this path being capable of being varied upon movement of the means for flexing the core.

The actual nature of this invention is best more fully explained or described by referring directly to the accompanying drawing. in FIG. 1 there is shown a transducer it; of the present invention designed for use as a phonograph pickup. This transducer includes an elongated re silient ferromagnetic bar 12, an end 14 of which is designed so as to be mounted rigidly in any sort of an appropriate clamping device (not shown) as, for example, a clamping device located within the pickup arm of a phonograph. The other end 16 of the bar 12 rigidly carries a stylus or needle 13 which may be mounted upon the bar 12 in any convenient known manner.

A small circular cavity 2% is located within the end 16 of the bar 12. A corresponding cavity 29 is also lo cated opposite the end 1'6 of the bar 12 within a pole piece 22 formed of ferromagnetic material. These cavities 2i? carry the ends of a non-metallic flexible core 24. Core 24, as further defined hereinafter is embedded with a ferromagnetic material dispersed throughout its mass. If desired, the ferromagnetic core 24 may be secured in place through the use of known conventional adhesives or the like. Preferably small pin-like projections 26 are formed upon the bar 12 and the pole piece 22 within the cavities 29 so as to engage the interiors of the ends of the core 24, firmly holding this core 2% in the desired location. Various other equivalent means serving to hold the core in place may be employed.

A pole 23 of a permanent magnet 35 is located against the pole piece 2?; in the transducer 1%, while the other pole 32 of this magnet 36 is located adjacent to, but spaced from the end 16 of the bar 12 a suficient distance so as to permit motion of this end 16 during the use'of the transducer. Brackets 34 for mounting purposes are preferably formed on both the magnet 39 and the pole piece 22 so that these parts may be rigidly secured in place as to an internal surface of a phonograph pickup arm through the use of screws, bolts or the like (not shown).

During the use of the transducer id current from an appropriate external source (not shown) is supplied to a coil as located around virtually the entire length of the core 24 through wires 38. Preferably this coil 36 is loosely disposed around the core 24 and is of a relatively rigid character; if desired, however, it may be somewhat fiexiblc and located in closer contact with this core. As the stylus i8 is moved, the core 24 will be deformed or flexed slightly; this in turn will cause a variation in the ferromagnetic path created by the magnet 3% so as to cause a change in the impedance of the coil 3o. With the transducer ill the spring-like or resilient character of the bar 12 will always return the stylus to a desired initial position. If desired, the bar 12 may be rigid and mounted by a pivot or universal joint (not shown) in such a way that the stylus it, is the only means capable of varying the reluctance path involved.

In order to permit maximum flexing of ferromagnetic core 2 in order to achieve a maximum change in the ferromagnetic path within the transducer 14 it is preferred to form this core 24 out of a resilient material, such as polychlorprene, rubber or the like, although, if

9 desired, the core 24 may be formed out of comparatively more rigid, yet flexible materials, such as polyethylene, nylon or various equivalents.

In FIG. 3 of the drawing there is shown a cross secional view of a modified transducer til which is essentially similar to the transducer 19. For convenience of description the parts of the transducer 4t"? which are substantially similar or identical to corresponding parts of the transducer iii are designated by the primes of the numerals previously applied, and are not separately designated.

In the transducer it) the pole piece 22. previously described is dispensed with and instead of this pole piece the magnet 3% is extended so that a pole 2.8 of it directly faces the end 16 of the bar 12'. This pole 23 is preferably directly provided with a cavity 29' and a projection as both as previously described.

In the transducer 453 the core 214' is created using any of the materials indicated in the preceding discussion of the core 24. In the transducer this core Ed is loaded with a plurality of discrete particles 42 of ferromagnetic material. This may also be the case with core 2d. These particles may consist of known iron alloys, ferrites or the like of non-permanent magnetic nature, all of which are capable of conveying or conducting magnetic flux. The proportions of such particles used will vary upon the nature of the material used in creating the core 24' prop- In general, as high a proportion of such particles should be used as is possible without deleteriously affecting the physical structure of the core 24' to a point Where this core is not structurally stable.

In PEG. 4 of the drawing there is shown a further modified transducer d l'of the present invention which consists of an elongated bar 46 adapted to be mounted in a similar manner to the bar 12 previously described. This bar contains a cavity 45 from the interior of which there extends a projection This cavity 48 is directly opposite a corresponding cavity 48 and a projection 59 located on a mounting bracket 52. This bracket 52 is preferably provided with an opening 53 designed to facilitate its being secured rigidly in place.

The cavity 4 3 and the projection t) engage or hold a core 54 Wl1il1 is substantially similar to the cores 24 and 24- previously described. This core 5d, however, is loaded with a plurality of discrete particles 56 of a permanently magnetized material. Suitable materials are permanent magnetic alloys, barium ferrite, and the like. If desired, these permanent magnetic particles 56 may be oriented so as to have poles located at the ends of the core 54, or they may be located in a random man- 'ner as far as magnetic orientation is concerned. Around the exterior of the core 54 there is located a wire coil 58 corresponding to the coil 36 previously described. This coil 58 is, of course, adapted to be connected electrically to the other equipment (not shown) through Wires 60.

When a stylus 62 connected to the bar 46 adjacent to the cavity 48 is moved up and down as by contact with a vertically modulated groove in a phonograph record a variation in the magnetic flux pattern created by the small permanent magnets 55 within the core 54 will occur. Such a change in flux pattern will be reflected in the impedence of the coil 58. I

If desired, it is possible to modify the transducer 4% so as to form both the mounting brac 6t 52 and the bar 46 out of a ferromagnetic material such as iron and to insert between them another bar of ferromagnetic material 64 such as is indicated in phantom in FIG. 4 of the drawing. This bar 64 is preferably spaced from either the bar 46 or the bracket 52 by a small space 66 as indicated so as to accommodate motion. Either the bar 64, the bracket 52 or the bar as or any combination of these may be permanently magnetized if desired so as to provide additional magnetic flux serving to drive the transducer 44:.

In FIG. 6 of the drawing there is shown a still further modified transducer 7d of the present invention Which is primarily designed to be used in obtaining eifects such as are commonly associated with stereophonic sound rcproduction. This transducer 7% includes an elongated resilient bar 72 formed out of iron or other equivalent ferromagnetic materials. This bar '72 has an end 74- which is adapted to be securely held by an appropriate mounting bracket (not shown). The other end 76 of this bar 72 carries a stylus '73 which may c secured in place by any convenient means.

The bar 72 is provided with internal cavities 3% which are disposed at a relationship with respect to one another on the exterior of this bar so that cores 82 similar to the cores 24 previously described are held withthese cavities so as to project at righ angles to o. e another. Sim'lar cavities tit) are located within porr iy T-shaped ferromagnetic mounting pole piece Ed. if desired, pr iections similar to the projections 26 previously described may be used in the cavities 3% so as to aid inholding the cores which may be impregnated with magnetic particles like the ferromagnetic particles previously described in connection with cores 2d and Cores may be impregnated with ferromagnetic particles as previously described in connection with cores 5d and 24.

The pole piece 8 is provided with mounting holes S? which are adapted to be used in securely mounting this pole piece in a desired position. A small permanent magnet is preferably attached to the pole piece 34 so as to extend from it toward the bar 72, but so as to have a surface 92 located from the bar 72 by a small space 94 suiiicient to accommodate movement between the magnet @d and the bar 72.

Such movement in the transducer it? occurs when the stylus 78 is moved back and forth or up and down within the grooves of a phonograph record or the like. Such movement causes a change in the magnetic reluctance path between pole piece 8d and bar 72. A current will be generated as a result within the coils 96 surrounding the cores 32;. By virtue of the fact that the two coils 96 are located at an angle with respect to one another the change in current in each of these coils will be different, due to the differential positions of end '76 with respect to pole piece 84 compressing one or elongating the other of cores 82.

It will be realized from the aforegoing description that the transducer 7% may be modified in various Ways as indicated in FIGS. 3 and 4 of the drawing so as to incorporate Within the cores 82 either ferromagnetic particles which are not permanently magnetized, or permanently magnetized particles of this type. In the latter case it is possible to obtain effects of the type desired by omitting from the structure the permanent magnet tl in which case 9% would designate an extension of polepiece It will also be realized that any of the transducers herein shown and described may be modified so that the cores used within them are held in place in different manners than the specific manner shown. The important thing within any of the transducers illustrated is to hold the cores in place so as to achieve the type of magnetic action inherent in the structures described in the preceding. It will also be realized that the basic features or principles of transducers embodied within the transducers it), 40, 44 and 76) may be embodied Within other differently appearing units used for phonographic reproduction or other purposes such, as pressure sensing or the like. If desired, the transducers described may be operated in a reverse manner so as to be driven so as to produce motion. When they are used in this manner current is, of course, supplied to the coils and in them so as to cause such motion. By appropriate adaptation of this type involving their use they can be employed as speakers, etc. Also, if desired, the magnets employed need not be permanent magnets. By appropriate operation of the coils used the parts described can be operated by magnetic flux created by these coils alone. Because of these facts this invention is to be considered as being limited only by the appended claims forming a part of this disclosure.

I claim:

1. A transducer which includes: a ferromagnetically loaded, non-metallic, flexible core having ends; means for rigidly mounting said core secured to one end of said core; means for moving said core secured to the other end of said core; coil means positioned around said core between said ends, and magnetic means for creating a magnetic field within said core, said magnetic means being fixedly attached to said means for rigidly mounting said core, and being spaced from said means for moving said core to form thereby a variable reluctance path, whereby movement of said means for moving said core will result in a variation in said field.

2. A transducer as defined in claim 1 wherein said magnetic means comprises permanent magnet means mounted adjacent to said ferromagnetically loaded, nonmetallic, flexible core, said permanent magnet means having pole means located adjacent to said ends of said core.

3. A transducer as defined in claim 1 wherein said magnetic means includes a plurality of permanently magnetized particles embedded within said flexible, nonmetallic core.

4. A transducer which includes: an elongated core of flexible non-metallic material including magnetic particles having ends, said core being formed out of a flexible elastomeric composition; a ferromagnetic pole piece secured to each of said ends of said core; means for rigidly mounting one of said pole pieces; means for transmitting motion to the other of said pole pieces; coil means positioned around said core between said ends; and permanent magnet means having poles, one of said poles being located in contact with said one of said pole pieces, the other of said poles being positioned adjacent to and spaced from said other of said pole pieces, permitting movement of said core.

5. A transducer as defined in claim 4 wherein said magnetic particles include a plurality of ferromagnetic particles located in said core.

6. A transducer as defined in claim 5 wherein said particles are permanently magnetized.

7. A phonograph pickup which includes: a flexible, non-metallic core including magnetic particles, said core having ends; means attached to one or" said ends of said core for rigidly holding said end of said core in place; a phonograph needle attached to the other of said ends of said core, said phonograph needle being capable of causing movement of said core when moved; coil means positioned around said core between said ends; and magnetic means for creating a magnetic field within said core, said field being capable of being varied in accordance with movement of said phonograph needle and said core.

8. A phonograph pickup as defined in claim 7 wherein said magnetic means comprises permanent magnetic means mounted adjacent to said core, said permanent magnet means having pole means located adjacent to said end of said core.

9. A phonograph pickup a defined in claim 7 wherein said magnetic means includes a plurality of permanently magnetized particles positioned within said core.

10. A transducer which includes: two flexible nonmetallic cores including magnetic particles located at an angle with respect to one another, said cores having adjacent moveable ends and fixed ends spaced from said moveable ends; a separate coil means positioned around each of said cores between the ends thereof; means for moving said cores secured to the movable ends thereof; and magnetic means for creating a magnetic field extending through each of said cores between the fixed and the movable ends thereof said magnetic means being fixedly attached to said fixed ends of said core and spaced from said means for moving said cores to form a variable reluctance path therebetween.

11. A transducer as defined in claim 10 wherein said magnetic means includes a pole piece attached to said fixed ends of said cores and a permanent magnet spaced from said movable ends of said cores.

12. A transducer which includes: an elongated bar formed out of ferromagnetic material, said bar having a fixed and a movable end; a phonograph needle attached to said movable end of said bar; a non-metallic flexible core including magnetic particles therein, one end of said core being attached to said movable end of said bar; means for rigidly mounting said other end of said core; coil means positioned around said core between the ends thereof; and magnetic means connected to said means for rigidly mounting and spaced from said bar, said magnetic means including permanent magnet means for creating a magnetic field extending through said bar and said core, said field extending between said ends of said core.

13. A transducer as defined in claim 12 wherein said permanent magnet means includes a plurality of permanently magnetized particles embedded within said core.

14. A transducer which includes an elongated bar formed out of ferromagnetic material, said bar having an end; two flexible non-metallic cores having magnetic particles therein, and being located at an angle with respect to one another, each of said cores having a movable end attached to said end of said bar and a fixed end spaced from said movable end; a separate coil means positioned around each of said cores between the ends thereof; means for rigidly mounting said fixed ends of said cores;

.. and magnetic means for creating a magnetic field extending through each of said cores between the ends thereof.

15. A transducer as defined in claim 14 wherein said magnetic means comprises: a permanent magnet, said permanent magnet having a pole located adjacent to and spaced from said bar.

References Cited by the Examiner UNITED STATES PATENTS 1,821,836 9/31 Hull 179-10041 2,348,352 5/44 Mallins 179-10041 2,499,110 2/50 Rich 179100.41 2,711,322 6/55 Dally 179100.41 2,864,897 12/ 58 Kaar 179-100.4l

IRVING L. SRAGOW, Primary Examiner.

ROBERT H. ROSE, JOHN P. WILDMAN, Examiners. 

1. A TRANSDUCER WHICH INCLUDES: A FERROMAGNETICALLY LOADED, NON-METALLIC, FLEXIBLE CORE HAVING ENDS; MEANS FOR RIGIDLY MOUNTING SAID CORE SECURED TO ONE END OF SAID CORE; MEANS FOR MOVING SAID CORE SECURED TO THE OTHER END OF SAID CORE; COIL MEANS POSITIONED AROUND SAID CORE BETWEEN SAID ENDS, AND MAGNETIC MEANS FOR CREATING A MAGNETIC FIELD WITHIN SAID CORE, SAID MAGNETIC MEANS BEING FIXEDLY ATTACHED TO SAID MEANS FOR RIGIDLY MOUNTING SAID CORE, AND BEING SPACED FROM SAID MEANS FOR MOVING 